1. Field of the Invention
The present invention relates to a method, system, and program for processing complexes to access shared devices.
2. Description of the Related Art
In certain computing environments, multiple host systems may communicate with a control unit, such as an IBM Enterprise Storage Server (ESS)®, to access data in a storage device managed by the ESS receiving the request. The ESS provides access to storage devices, such as interconnected hard disk drives through one or more logical paths. (IBM and ESS are registered trademarks of IBM). The interconnected drives may be configured as a Direct Access Storage Device (DASD), Redundant Array of Independent Disks (RAID), Just a Bunch of Disks (JBOD), etc. The control unit may include duplicate and redundant processing complexes, also known as clusters, to allow for failover to a surviving cluster in case one fails.
Two processing complexes in a control unit may share certain devices, such as adaptors that provide connections to the hosts or storage systems. The processing complexes may communicate with each other to coordinate their sharing of adaptors. In the event that communication is lost between the processing complexes, each processing complex, to the extent possible, will race to obtain a lock to the shared adaptors. The processing complex accessing the lock first will have exclusive access to the shared adaptors and the processing complex losing the race will have access to no adaptors and may go off-line. The lock is held exclusively by the processing complex winning the race to access the lock until communication is reestablished between the processing complexes, at which point the lock is set to a free state where both processing complexes may access the shared adaptors and coordinate their access.